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From: mislan@cspi.com (David Mislan)
Newsgroups: comp.graphics,comp.sys.ibm.pc
Subject: Re: Print a 75 ppi image on a 300 ppi laserprinter
Keywords: Alogarithsm to show the depth
Message-ID: <410@cspi.cspi.com>
Date: 5 Oct 89 15:32:11 GMT
References: <814@dukempd.phy.duke.edu>
Reply-To: mislan@cspi.UUCP (David Mislan,Michel Marcuse)
Organization: CSP Inc., Billerica, MA
Lines: 31


	There are two methods you can use to render grayscale level images
on a binary output device such as a laser printer: half-toning and
dithering. Half tone consists of using, for instance, a 6x6 square on the
printer to represent each pixel in the image. By printing or leaving blank a
certain number of pixels,different gray levels can be obtained (in this case,
37, which should be adequate for most applications). The problem with this
is that you may not be able to fit large images on the page.

	The second technique is called dithering and is meant to use one dot
per pixel. This technique works well for large images, but you will lose some
detail, in particular on small images. 

	For a better description of these very useful techniques, let me refer
you to the classic computer graphics text "Fundamentals of Interactive Computer
Graphics" by J.D. Foley and A. Van Dam, chapter 17 (Addison-Wesley publishers
Library Catalog no. T385.F63)

	You will most certainly need to expand the memory on your laserjet
to print large images. (The way it was explained to me is that the printer 
needs to have all of the data in memory prior to printing the page).


						Michel L. Marcuse
						Sr. Software Engineer,
						Scientific Imaging Division
						CSPI.

---
Disclaimer:	The opinions expressed herein are mine only and do not reflect
                those of my employer.